1. Field of the Invention
The invention relates to a deflection measuring device according to the interferometer principle having a radiation source, a first fiber-optic means implementing a first light path, a second fiber-optic means implementing a second light path, a deflection body and an evaluation circuit, wherein the first fiber-optic means and the second fiber-optic means can be impinged with interference-capable radiation from the radiation source on the input side, wherein at least the first fiber-optic means is connected with the deflection body and wherein the first partial radiation guided in the first fiber-optic means and the second partial radiation guided in the second fiber-optic means are brought together on the output side and the interference radiation is conveyed to the evaluation circuit and evaluated by the evaluation circuit.
2. Description of Related Art
Deflection measuring devices using the interferometer principle have been known for quite some time in the prior art and are used everywhere where mechanical deflection of a deflection body have to be received and acknowledged with great sensitivity. Applications can be found, for example, in the field of vibration measuring devices that are based on repeating or also periodic deflection of a deflection body, wherein the deflection of the deflection body is either heteronomous by a physical process—e.g., in vortex flow measurement—or wherein a deflection of the deflection body is stimulated and the actual value of interest consists in the damping of the stimulated oscillation—e.g., in viscosity measurement. In other measuring tasks, the degree of deflection of the deflection body is of interest, such as, for example, in the metrologic detection of the deflection of a membrane in pressure or differential pressure measurement.
Fiber-optic interferometry is thus, inter alia, of advantage because very small deflections can already be detected, namely deflections that lie in the (sub-) wave range of the used radiation. As is known, two sufficiently temporal coherent—i.e., capable of interference—beams are brought to overlap by an interferometer. Normally, the radiation of the—coherent—radiation source is split with a first beam splitter and a second beam splitter, wherein the partial beams, in the case of the application seen here, are guided from fiber-optic means via these fiber-optic means. The light paths of the first partial beam and the second partial beam implemented by the fiber-optic means are also called the arms of the interferometer. At the exit of the interferometer, the partial beams are brought together and brought to interference. The radiation intensity at the exit of the interferometer is proportional to the cosine of the phase difference between both interfering partial beams. Changes in the phase difference, e.g., caused by the smallest changes of the length of an interferometer arm, result in a detectable change in intensity at the exit of the interferometer, wherein the change in length in the present case is based upon in that one of the light paths is guided over the deflection body so that a deflection of the deflection body immediately takes effect on the length of the light path and is, thus, detectable. The term “fiber-optic means” is not to be understood here in a restrictive sense of waveguides, however, it could be a waveguide. For example, different cores within a light waveguide can be meant by a fiber-optic means.
Mach Zender interferometers are often used as the interferometer, but other types of interferometers also come into question, for example, the Michelson interferometer. In order to create the radiation used in the interferometer, semiconductor lasers are particularly suitable as a radiation source. Even when light paths are being discussed here, which are implemented with the fiber-optic means, visible electromagnetic radiation should not be understood in a restrictive manner, but can mean any electromagnetic radiation as long as it is suitable for fiber-optic applications in the field of interferometry.
The high sensitivity of the interferometric measuring method, however, does not only have advantages, but also disadvantages, which, due to high sensitivity, always has the risk that undesired disturbance signals are created, which often occurs in the rough surroundings of process measurement. Here, the problem is that the deflection body with the first or second fiber-optic means attached on it has to be arranged close to the detecting process, whereas the evaluation circuit should be arranged as far as possible from the process, such as in high temperature or high pressure applications. In addition to the evaluation circuit, the optical couplers used are also often sensitive in terms of thermal and mechanical stress, wherein the optical couplers form the interaction sites of the first and the second fiber-optic means. When the optical coupler has to be arranged far away from the physical process to be detected by measurement, it is necessary that a very large extension of the light path formed by the first fiber-optic means and by the second fiber-optic means occurs. However, this also means that the area sensitive to deflection is not only limited to the deflection body, but also to a possibly wide-stretched supply area of the deflection body, which can be a problem for the reasons described above.